1. Technical Field
The present disclosure relates to a sealing epoxy resin composition, a hardened product of this composition, and a semiconductor device sealed with the resin composition.
2. Background Art
In general, semiconductor elements such as transistors, ICs, and LSIs are sealed with an epoxy resin composition so as to be used as semiconductor devices. Such plastic packaging protects the semiconductor elements from external environment or improves their handling ability.
It is a common practice to add a hardening accelerator to the epoxy resin composition in order to accelerate the hardening reaction to form a hardened product. Examples of the hardening accelerator include the following: nitrogen-containing heterocyclic compounds, phosphine compounds, quaternary ammonium compounds, quaternary phosphonium compounds, and arsonium compounds. Examples of the nitrogen-containing heterocyclic compound include amines, imidazole compounds, and 1,8-diazabicyclo[5.4.0]undecene-7.
Epoxy resin compositions containing quaternary phosphonium compounds have particularly excellent moisture-resistance reliability and preservation stability. These compositions therefore are used in thin packages as a sealing material required to have high fluidity. One of the most commonly used quaternary phosphonium compounds is tetraphenylphosphonium tetraphenylborate (hereinafter, TPPK).
The TPPK is, as it is, very stable and catalytically inactive. Therefore, it is previously heated with a phenol resin in order to produce a phenol resin salt, which is added to the epoxy resin composition. However, the production of the phenol resin salt from the TPPK generates trace amounts of benzene and causes environmental pollution when the benzene is released to the environment from the resin composition.
As a hardening accelerator that does not cause such problems, there has been proposed a phenol resin salt of alkyl quaternized phosphonium, which is derived from triphenylphosphonium (hereinafter, TPP) (see Japanese Unexamined Patent Application Publications No. 2004-256643 (PLT1) and No. 2005-162944 (PLT2)).
As another hardening accelerator, a phosphonium salt in the form of particles is proposed to ensure the fluidity of the epoxy resin composition when melted (see Japanese Unexamined Patent Application Publications No. 2006-124643 (PLT3) and No. 2007-119710 (PLT4)).
Furthermore, Japanese Patent No. 4429768 (PLT5) discloses a method of producing an intermediate composed of a quaternary phosphonium cation and an organic carboxylate anion.